Bp 300

All RFB and SFB measurements were carried out in a custom modified N₂ flush box (Terra Universal) with continuous N₂ purging. 5.0 mL solution of 0.2 M BTMAP-Fc and 5.0 mL solution of 0.2 M BTMAP-Vi, both with 1.0 M NaCl as the supporting salt, were used as anolyte and catholyte, respectively. Both BTMAP-Fc and BTMAP-Vi were purchased from the Tokyo Chemical Industry Co., Ltd. and used directly. The N^Me-TEMPO was synthesized following a previous report^{50 (link)}. The electrolyte flow rate was set from 20 to 120 mL min⁻¹ for RFB measurements. Galvanostatic cycling tests were carried out using a Bio-Logic BP-300 potentiostat at desired constant current densities with 0.3 and 1.1 V as the bottom and top potential limits, respectively. A 10 s rest period at open-circuit voltage was employed between each half cycle. The potentiostatic capacity of the RFB was determined by galvanostatic charging/discharging followed by a potential hold at cut-off potentials until the current density reached 1 mA cm⁻².

Totally, 5.0 mL solution of BTMAP-Vi/Fc with concentrations of 0.1 and 0.2 M in 1.0 M NaCl, or 5.0 mL solution of BTMAP-Fc/ N^Me-TEMPO with concentrations of 0.1 M in 1.0 M NaCl were used as the catholyte/anolyte. The electrolyte flow rate was controlled at 40, 60, and 80 mL min⁻¹ for the SFB cycling tests. A dual-channel Bio-Logic BP-300 potentiostat was used for the SFB cycling tests. To characterize the charging–discharging behaviors of the integrated SFB device, one potentiostat channel (CH1) was configured as the RFB mode to monitor the potential between the two carbon felt electrodes; the other potentiostat channel (CH2) was configured as solar recharge mode to monitor the charging photocurrent (Fig. 1c).
During the solar charging process, the GaAs photoelectrode was illuminated by one Sun simulation (as described in the PEC characterization section) without applying external bias. A 1.35 h time limit was used to control the SOC below ca. 54%. During the discharging process, the illumination was blocked by a beam shutter, and a discharging current intensity of 11 mA was applied by CH1 until the cell potential reached 0.3 V. The dual-channel potentiostat and the beam shutter of the solar simulator were synchronized and controlled by CH1 and a custom-made electronic control box to enable automated long-term SFB cycling measurements.

UV–vis absorption spectra
were collected using an Ocean Optics UV–vis spectrometer with
a DH-2000 BAL dual source (deuterium and tungsten) and OCEAN-FX-XRI-ES
diode array detector. Electrochemical measurements were recorded on
either a Biologic SP 300 or Biologic BP 300 potentiostat. FTIR spectra
were collected using a Bruker Alpha FT-IR spectrometer with a Pt-diamond
single-bounce ATR cell and a DTGS detector.